Process and preparation for heat treating of steel



Patented Nov. l6, 1943 PROCESS AND PREPARATION FOR HEAT TREATING OFSTEEL Joseph H. Schmitt, Rumson, N. J., assignor to Edna I. Bcekman,Washington, D. 0., and Jo.- seph H. P. Schmitt, Rumson, N. J.

No Drawing. Application April 22, 1941,

Serial No. 389,754

Claims. ('01. 148-30) This invention relates to an improved process andpreparation for heat treating of steel.

In heat treating steel it is desirable that the degree of carburizationand of carbon penetration be varied depending upon the qualities whichit is desired to obtain in the steel. Controlling the treatment so as toobtain the desired percentage of carburization and depth of penetrationand so as to obtain the desired degree of uniformity in carburization isexceedingly difficult and presents many problems.

It is the object of the present invention to overcome the problems anddiificulties heretofore encountered, and to provide an improved processand preparation for heat treating of steel which enables the operator tocontrol in a relatively simple and convenient manner the percentage ordegree of carburization and the depth of penetration, and to provide asubstantially uniform degree of carburization.

A further object is the provision of an improved preparation of theabove character which may be packed, transported and stored in liquidform for convenience in handling. but which is converted into gaseous orvapor phase when introduced into a heat treating chamber so as toprovide the desired type of atmosphere. By varying the proportions ofthe components employed, as hereinafter described, the gaseous or vaporatmosphere thus provided, may vary from a substantially neutralatmosphere to an atmosphere which is of a highly carburizing character.

In carrying out my invention, I propose to provide a preparation whichmay be packed, trans ported and handled in liquid phase, but which willchange to a vapor or gaseous phase when subjected to heat treatingtemperatures in the range of 1500 F. or higher. This preparationconsists primarily of a mixture of two other components. The first ofthese components is a liquid hydrocarbon carburizing agent which willvaporize, decompose and crack when introduced into a heat treatingchamber at' heat treating temperatures to release carbon monoxide (CO)and carbon dioxide (CO2) in such proportion as to cause carburization ofthe steel being treated.

The second component may .be referred to, for

convenience, as an oxidizing agent and is a material which, whenintroduced into a heat treating chamber at heat treating temperatures,wili release free oxygen and will thereby serve as an oxidizing agent tooxidize the carbon resulting from decomposition or cracking to producecarbon monoxide (CO) and carbon dioxide (CO2).

while excess of oxygen over precipitated carbon to produce her at heattreating temperatures so as to produce a carburizing atmosphere.Examples of this type of material are the aliphatic alcohols such asethyl, methyl, propyl and butyl alcohol, and also dipentine. Variousliquifiable members of the paraffln series may also be employed in whichevent those materials which are in gaseous phase under normalatmospheric conditions may be compressed to produce a liquid for theconvenience of packing, transportation and use.

In determining which materials are suitable for use as a carburizingagent, I have found that the material should be one that can be handledand shipped in liquid phase and which, when subjected to heat treatingtemperatures in a heat treating chamber, will vaporize and crack toproduce an atmosphere having both carbon monoxide and carbon dioxide init, the carbon monoxide being in a proportion in excess of 12 /2 arts to1 by volume of the carbon dioxide. In this connection I have found thatcarburization take place when the carbon monoxide is in excess ofsubstantially 12 parts to one part of carbon dioxide and that themaximum degree of carburization takes place when the atmosphere includescarbon monoxide in the proportion of substantially 45 parts to 1 byvolume of the carbon dioxide present.

As the second component of my preparation I may employ any materialwhich is in liquid phase or which can be converted into liquid phase forshipping and handling, and which is cracked or chemically decomposedwhen subjected to heat treating temperatures in a heat treating chamberso as to release free oxygen. For this purpose I prefer to employnitro-methane.

The two components may be mixed together in such proportions that whenthey are introduced into a heat treating chamber at heat treatingtemperatures, they will produce an entirely neutral atmosphere or, byVary g the proportion they will be caused to produce a highlycarburizing atmosphera' By decreasing the percentage of the secondcomponent or oxidizing agent, the carburizing characteristic of theatmosphere is increased. By increasing the proportion of the secondcomponent, the carburizing characteristic of the atmosphere isdecreased.

When the percentage of components are so arranged that the atmosphereresulting in the heat treating chamber at heat treating temperaturescontains carbon dioxide and carbon monoxide in the proportion ofsubstantially 45 parts to 1 by volume of carbon monoxide to carbondioxide, the highest degree oi! carburization is obtained. On the otherhand, by arranging the proportions of components so that the atmospherecontains less than 12 /2 parts of carbon monoxide by volume to each partof carbon dioxide, a substantially neutral atmosphere is obtained. Theproportions may alsobe varied to obtain any degree of carburizationwhich may be desired between these two extreme limits.

1 Mom specific example of the components that may be used in mypreparation, I may employ butanol, or butyl alcohol as the firstcomponent or carburizing agent. As the second component or oxidizingagent, I may employ nitro-methane.

Both of these materials are in liquid phase under normal atmosphericconditions, and are readily mixable with each other in any desiredproportions. When butanolis introduced into a heat treating chamber atheat treating temperature, it will vaporize and crack to produce acarburizing atmosphere. When nitro-methane is introduced into a heattreating chamber at heat treating temperature, it likewise will vaporizeand break down, releasing free oxygen.

The proportions of the butanol and nitromethane in the preparation maybe varied. When substantially 30 percent by volume of butanol, and 70percent by volume of nitro-methane are mixed together, the resultingpreparation produces a neutral atmosphere when introduced into a heattreating chamber at heat treating temperatures, which will neithercarburize or oxidize the steel being treated. When substantially 90percent 01 butanol and-'10 percent of nitro-methane are mixed together,the resulting preparation when introduced into a heat treating chamberat heat treating temperatures, produces an atmosphere having the highestcarburizing characteristic.

Varying the proportions between these two extreme results inpreparations producing atmospheres having varying intermediatecarburizing characteristics. Decreasing the percentage of ultra-methanebelow percent also results in decreasing the carburizing characteristic.

In using my improved preparation the two components are mixed togetherso .as to produce a liquid preparation having the desired carburizingcharacteristic. Dueto the fact that the preparation is in liquid form,it may be conveniently packed, transported, stored and used.

1 In the heat treatment or steel. the steel is treated in the usual heattreating chamber and the preparation is introduced into the chamber inliquid form in some suitable fashion as by dropping it or spraying itin. The heat treating temperature causes the preparation to vaporize,decompose and crack, producing an atmosphere having the desired neutralor carburizing characteristic depending upon the proportions of thecomponents used in the preparation. Various types of, heat treatingpreparations having difierent carburizing characteristics will berequired, and those skilled in the art will readily be able to selectthe preparation having the desired neutral or carburizingcharacteristic. By increasing the percentage of butanol to substantially90 percent, an atmosphere is produced having a high carburizingcharacteristic having approximately 45 parts of carbon monoxide to 1part or carbon dioxide. By increasing the proportions or nitromethane toapproximately 70 percent, the proportion of carbon monoxide is decreasedto less than 12 parts of carbon monoxide to each part I p'onents may beintroduced simultaneously into the chamber without being first mixedtogether. Various modifications may, of course, be made in the describedembodiment of my invention without departing from the invention as setforth in the accompanying claims.

I claim: 1. A preparation for use'in heat treating steel comprising aliquid mixture of butanol and nitromethane.

2. A preparation for use in heat treating steel comprising a liquidmixture of butanol and nitromethane, the nitro-methane comprising nomore than substantially 70' percent of the mixture.

3. A preparation for use in heat treating steel comprising a liquidmixture of approximately 30 percent butanol and approximately '70percent nitro-methane.

4. A preparation for use in heat treating steel comprising a liquidmixture or between approximately 30 and percent 01' butanol and between.

'10 and 10 percent of nitro-methane.

JOSEPH H. SCHMITT.

